Pressure sensitive adhesives are widely used for a multitude of purposes, such as various sealing and attachment applications. Many attachment applications utilize supported adhesive systems, which generally are comprised of a support material, formed as a sheet or elongated tape, which is faced, often on both sides, with adhesive coating. For bonding together paper sheets or the like a relatively thin support material, such as a plastic film, generally suffices. For bonding larger objects, or where the surfaces being bonded together, or one of them, is contoured or uneven or textured, supported adhesive systems having a more substantial thickness are generally more suitable. The thickness of the system, together with some degree of elasticity, provides some conformity of the sheet or tape to the surfaces being bonded, permitting the adhesive coating to more universally contact such surface(s) along the entire length and breadth of the sheet or tape being applied.
Many applications require a relatively thick adhesive system that is also extremely durable, such as the automotive industry trend towards use of pressure sensitive adhesive tapes for attachment of automotive trim items such as vehicle side moldings, insignia, and the like, instead of mechanical attachments that require vehicle body perforations, because such perforations may lead to corrosion problems. In addition, the use of pressure-sensitive adhesive bonding for such automotive applications, if it can be applied with reasonable ease, permits selection and application of trim items after the vehicle leaves the manufacturer. Given the stresses normally placed on such trim items over years of vehicle use, durability of the form of attachment is extremely important.
U.S. Pat. No. 4,233,067 discloses a pressure-sensitive adhesive tape having a thickness exceeding 0.2 mm which contains a filler of glass microbubbles within the adhesive material matrix, as an improvement with respect to durability and cost regarding relatively thick adhesive systems. Such tapes may have unfilled adhesive coatings, and the adhesive material(s) are polymeric composition, ideally formed by ultraviolet light initiated polymerization in the presence of the filler. In such polymerizations, the polymerizable mixture and microbubbles must be sufficiently transmissive to ultraviolet light.
In the automotive industry, and other industries using relative thick pressure-sensitive adhesive systems for attachment purposes, it is considered very desirable to conceal the presence of adhesive tape or sheet. For instance, when used to attach automotive trim items, the edge of the adhesive system is generally exposed, and hence tapes having a camouflaging color are highly desirable. The best camouflage by virtue of color would of course be a color that matches the trim item being attached or the surface to which it is attached. Automotive vehicles are produced with a multitute of body colors, and trim items may also be used of an unlimited variety of colors, although the most often used color for side-moldings and the like is black. A significant disadvantage inherent in adhesive tapes having a glass microbubble filler is that, by virtue of optical effects, the color of such tapes is white. Moreover, if produced by ultraviolet light initiated polymerization, only a small amount of carbon black, the typical substance used to impart a black color to a pressure-sensitive adhesive system, may be incorporated into the tape because carbon black interferes with such polymerization method. It is believed that at best, using ultraviolet light initiation of the polymerization, only a grey color can be achieved by the incorporation of carbon black to the extent possible.
U.S. Pat. No. 4,612,242 discloses a glass microbubble filled pressure sensitive adhesive tape, the appearance of which is darkened by coating the microbubbles, prior to incorporation into the system, with a thin-film of, for instance, silver, wherein such coating is sufficiently thin not to unduly inhibit polymerization of the adhesive matrix by ultraviolet light techniques. U.S. Pat. No. 4,666,771 discloses a glass microbubble filled pressure sensitive adhesive tape with a darkened appearance by virtue of using stained glass microbubbles and adding a pigment or dye to the adhesive matrix, which requires for photopolymerization that the stained glass microbubbles have an ultraviolet light window. These techniques to darken a glass microbubble filled adhesive tape are significantly elaborate and thus believed to require sophisticated and expensive manufacturing procedures.
It is an object of the present invention to provide a pressure-sensitive adhesive system that provides a color-camouflage type of concealment without elaborate manufacturing techniques. It is an object of the present invention to provide such a system that may be formed using ultraviolet light initiation of the polymerization in the presence of the filler. It is an object of the present invention to provide such an adhesive system that does not compromise the durability of bonding provided generally by filled pressure-sensitive adhesive taped. These and other objects and advantages of the present invention are described below.